Summary: DNA microarray hybridization is used to identify different viruses and viral strains. During this year it has been used to to study the following groups of microorganisms: Rotaviruses: A microchip was created for genotyping human rotaviruses prevalent in the Unites States. A blind study condicted with NIAID/NIH has shown that the method correctly identified 100% of viral isolates. Orthopox viruses: A microchip based on viral B29R gene sequences was created and used for discrimination among members of Orthopox viruses group, including monkeypox, vaccinia, rabbit pox, etc. Pathogenicity factors in enteric bacteria. A microchip was created to identify six pathogenicity factors in E.coli and other enteric bacteria. This part of the project was done in collaboration with CFSAN. Poliovirus. A microchip to study genetic maps of recombinant poliovirus was developed. It allows a high-througput analysis of vaccine-derived polioviruses that partially reverted to virulence.